Ok, this one is extremely crazy! As the peon says, "Work, work!"
You need to do a couple of big expansions...use this: http://www.wolframalpha.com/widget/widgetPopup.jsp?p=v&id=6767c31553b5f2c292b426c97a9b6013&title=Binomial+Expansion+Calculator&theme=blue&i0=a%2B2b%2B3x&i1=6&podSelect&includepodid=Input&includepodid=